This invention relates to an improvement in a shaft clamping device and particularly to a shaft clamping collar of a type adapted to grip a shaft without marring or otherwise damaging its surface. This type of shaft clamping device usually provides substantially greater holding power than set screw type shaft collars.
To obtain normally required high holding power while utilizing a collar having a relatively small outside diameter to save material, split type shaft couplings or collars utilizing cap screws for the clamping force conventionally permit the head of the cap screw(s) to extend past the outer periphery of the coupling or collar. This practice, however, can result in a safety hazard when the collar is used as a power transmitting device that is unshielded.
If space is not critical in a particular application, and added cost can be tolerated, a collar having an oversized outside diameter can be used. However, normally, both space and cost are significant considerations. Where space is critical and high holding power is required, as in a transmission application, an oversized outside diameter collar likely will not fit; a standard size collar specified for the specific applied load may require extra clearance to accommodate the standard screw head extending beyond the periphery of a standard collar which may well be prohibitive and thus require the portion of the screw head extending past the collar to be ground away. This practice makes loosening or removal of such a clamping device extremely difficult.
To resolve such problems, efforts have been made using differential clamping screws, e.g., for expanding and contracting the diameter of the clamping surface of a collar such as illustrated in U.S. Pat. No. 3,876,318 issued Apr. 8, 1975 to Corey F. Crispell. Such constructions, however, are expensive.
Other efforts have been made to provide shaft clamping devices, such as illustrated in U.S. Pat. No. 3,917,424 issued Nov. 4, 1975 to Martin J. Zugel, wherein the head of the clamping screw is encompassed within the outer wall of the collar. It has been the applicant's experience that when such constructions are used in a collar of relatively small outside diameter to save material and space while providing a standard clamping screw for the required holding power, highly developed stress concentrations are experienced at the junction between the clearance hole for the clamping screw head and its bearing area, resulting in frequent failure of collars under specific applied loads.
Further efforts to overcome the above described deficiencies have included the use of clamping screws which are one or even two sizes under size. These efforts have resulted in greatly reducing the effectiveness of the clamping device and require use of significantly larger collars to hold specific loads which cannot meet dimensional limitations in certain applications.
Accordingly, it is an object of this invention to provide a new and improved shaft clamping device which achieves seemingly incompatible objectives in assuring that its clamping screw is housed entirely within the periphery of a collar which is of a smaller diametrical size relative to the size collar required to encompass a standard size screw normally specified for the required holding power of the device.
A further object of this invention is to provide a new and improved collar of the above described type having significantly increased strength and resistance to failure. Included in this object is the aim of providing such a collar particularly suited to be used with a clamping screw which when seated is maintained within the periphery of the collar which effects a holding power normally achieved only with a standard size screw which would project beyond the collar periphery.
Another object of this invention is to provide such a collar which features a junction between a screw head clearance hole in the collar and the bearing area providing for reduced stress concentration and resulting in a collar of significantly increased strength in what is normally considered its weakest region.
Other objects will be in part obvious and in part pointed out more in detail hereinafter.
These and related objects are achieved in accordance with this invention by providing a shaft clamping device which utilizes a unique resilient annular collar having a circular opening therein and a radial slot extending from the opening, the collar having a tapped opening on one side of the slot and a coaxially aligned recess on the opposite side of the slot, the recess having a relatively enlarged entrance and a relatively reduced clamping screw clearance hole, the recess further including a tapered diameter surface defining a junction between the entrance of the recess and its clearance hole to effect reduced stress concentration under clamp loading.
A better understanding of the invention will be obtained from the following detailed description and the accompanying drawing of an illustrative application of the invention.